Amplifying system



Oct. 16, 1928. 1,687,540

w. L. CARLSON AMLIFYING SYSTEM Filed Dec. 22, 1925 Inventor: Wendell L. Carlson,

by M Hi5 Attorney Patented 16, 1928.

UNITED STATES PATENT OFFICE.

wmm IL 65318011, 01 BCHEN'ECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIO GOIPAKY, A CORPORATION OF NEW YORK.

Amman: G SYSTEM.

Application filed December 22, 1925. Serial No. 77,111.

My present invention relates to systems for amplifying high frequency currents, and more particularly to systems employing a plurality of thermionic amplifiers connected in cascade.

It is well known that where a plurality of thermionic amplifiers are connected in cascade there is a tendency for the production of oscillations in the system by reason of feedback. The feed-back which tends to produce oscillations may be of different kinds. It may be magnetic or electrostatic by reason of the location of the different circuits with respect to one another, and in case common batteries are employed for supplying the heating current to the cathodes of the devices in parallel and common plate batteries are employed, a resistance coupling due to the internal resistance of the batteries and the resistance of the cathode elements is introduced which will sometimes produce a feed-back sufiicien't to cause the production of oscillations.

My present invention relates to feed-backs caused by'resistance coupling. The ob ect of my invention is to provide a means whereby the effect of this resistance coupling feedback may be eliminated to prevent the production of objectional regeneration or oscillations. V

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation will best be understood by reference to the following description taken in connection with the accompanying drawing in which I have illustrated diagrammatically a circuit arrangement which may be employed in carrying my invention into efl'ect.

I have indicated in the drawing a radio receiving and amplifying system of the super-heterodyne type This system comprises a first tlllefymtecmr tllllbe 1, initermediats r uen amp' gtu es2an 3,secon de tiictor tube 4, audid frequency amplifier tube 5, and an oscillator tube 6. Signals received upon the receiving loop 7 are imprwed upon the input or grid circuit of the detector tube 1, together with 'oscillations produced by the oscillator tube 6, through an adjustable coupling transformer 8. The resultant or intermediate frequency current produced in the output circuit of detector 1 is impressed upon the input circuit of amplifier 2 and amplified by the amplifiers 2 and 3 in the usual manner. The amplified current from the output circuit of tubes 2 and 3 impressed on the input circuit of detector 4.

A common battery 9 is employed for supplying heating currents to the cathodes of all of the tubes in parallel, and the common batteries 10 and 11 supply plate currents to all of the tubes in parallel. It is well known that high frequency currents are present in the output circuit of detector 4 in such an arrangement, and in the absence of any means for preventing it such a current will produce a voltage drop across the plate battery 10 due to its internal resistance, and this voltage drop will be applied to the plate circuit 0t tube 1 and through the coupling transformer 12 to the input circuit of tube 2. The resulting feed-back may be suilicient to cause the production of oscillations in the system.

If now a condenser 13 is connected in shunt between the plate 4 and one side of the cathode, the high frequency voltage will be by-passed directly from the plate to cathode and the resistance plate battery coupling will no longer impress a high frequency voltage upon the circuit of, tube 1. With the single condenser 13, however, there will still exist an appreciable high frequency voltage drop through the resistance of the cathodes. The plate current through the condenser 13 will divide at the cathode terminal, most if it going directly into the cathode of tube 4, but some of it passing through the cathode battery 9 and associated resistance 15, and a small portion flowing through the cathode of tube 1, and thence to the opposite side of the cathode of tube 4. Thus a high frequency voltage will be impressed upon the plate circuit of tube 1 due to the difi'erence of the high frequency potential existing between the two ends of the cathodes of tubes 4 and 1. This voltage which is transferred directly to the plate circuit of tube 1 will be extremely small, but when backed up by the high degree of amplification of the intervening amplifier stages it may have the elfect of creating objectionable regeneration or oscillation in the amplifier system as a. whole. I have found that by connecting a second'condenser 14 of the same capacity as condenser 13 from the plate of divide equally through capacities 13 and 14 and the high frequency potential of both sides of the filament will be the same. No high frequency current from tube 4 will flow throu h the cathode of tube 1, consequently no vo tage will be induced in the plate circuit of tube 1 through a resistance coupling due to the fact that the cathodes are connected in parallel.

While I have shown and described a pre- 15 ferred form of my invention, it will be apparent that many modifications in the manner in which it is carried out may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is 1. The combination in a signal amplifying system of a plurality of electron discharge amplifiers connected in cascade for amplifying radio frequency currents, a detector connected to detect the amplified radio fre. quency currents, common batteries for supplying cathode heating currents and plate currents to all of said amplifiers and said detector in parallel, and a air of capacities connected in shunt from t e plate to opposite terminals of the cathode of said detector for preventing a feed-back to the input cireuits of the amplifiers by reason of resistance coupling due to the use of common batteries.

2. The combination in a signal amplifying system of a plurality of electron discharge amplifiers connected in cascade for amplifying radio frequency currents, a detector connected to detect the amplified radio frequency currents, common batteries for supplying cathode heatin currents and plate currents to all of sai amplifiers and said detector in parallel, and a pair of capacities connected in shunt from the plate to opposite terminals of the cathode of said detector and in shunt to the battery which supplies plate current to the detector for preventing a feed-back to the input circuits of the amplifiers by reason of resistance coupling due to the use of common batteries.

In witness whereof, I have hereunto set my hand this 21st day of December, 1925.

WENDELL L. CARLSON.

CERTIFICATE OF CORRECTION.

Patent No. 1,687,540.

WENDBLL L.

Grsntsd 0mm 16. ms, to

causes.

It is hereby certified that error appears in the printed specification of the above Indicted pstsnt requiring correction as follows: Page 1, line 60, alter the amoral "3", insert the word "is", all line9l, for the word "if" rend "of"; and that the said Letters Patent should he rend with these corrections therein that the sauna may center. to the record of the ease in the Patent sa e and and mi. um a of 1mm, A. a. 1m.

ll. J. Moore. Acting Connnissioner of Patents.

tube 4 to the osite side of the filament,

this objectionah e resistance coupling is eliminated. With this arrangement the high frequency plate current of tube 4 will 5 divide equally through capacities 13 and 14 and the high frequency potential of both sides of the filament will be the same. No high frequency current from tube 4 will flow throu h the cathode of tube 1, consequently no vo tage will be induced in the plate circuit of tube 1 through a resistance coupling due to the fact that the cathodes are connected in parallel.

While I have shown and described a preferred form of my invention, it will be apparent that many modifications in the manner in which it is carried out may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is 1. The combination in a signal amplifying system of a plurality of electron discharge amplifiers connected in cascade for amplifying radio frequency currents, a detector connected to detect the amplified radio fre. quency currents, common batteries for supplying cathode heating currents and plate currents to all of said amplifiers and said detector in parallel, and a air of capacities connected in shunt from t e plate to opposite terminals of the cathode of said detector for preventing a feed-back to the input cireuits of the amplifiers by reason of resistance coupling due to the use of common batteries.

2. The combination in a signal amplifying system of a plurality of electron discharge amplifiers connected in cascade for amplifying radio frequency currents, a detector connected to detect the amplified radio frequency currents, common batteries for supplying cathode heatin currents and plate currents to all of sai amplifiers and said detector in parallel, and a pair of capacities connected in shunt from the plate to opposite terminals of the cathode of said detector and in shunt to the battery which supplies plate current to the detector for preventing a feed-back to the input circuits of the amplifiers by reason of resistance coupling due to the use of common batteries.

In witness whereof, I have hereunto set my hand this 21st day of December, 1925.

WENDELL L. CARLSON.

CERTIFICATE OF CORRECTION.

Patent No. 1,687,540.

WENDBLL L.

Grsntsd 0mm 16. ms, to

causes.

It is hereby certified that error appears in the printed specification of the shove Indicted pstsnt requiring correction as follows: Page 1, line 60, alter the amoral "3", insert the word "is", all line9l, for the word "if" rend "of"; and that the said Letters Patent should he read with these corrections therein that the sauna may center. to the record of the ease in the Patent sa e and and mi. um a of December, A. a. 1m.

ll. J. Moore. Acting Connnissioner of Patents. 

